1. Field of the Invention
The present invention relates generally to an ink-jet printing apparatus and a test printing method. More specifically, the invention relates to an ink-jet printing apparatus for performing printing by ejecting an ink and a hypochromic or achromatic liquid for making the coloring agent in the ink insoluble or coagulating the coloring agent, on a printing medium, and a test printing method therefor. The present invention is applicable for all devices employing printing media, such as paper, cloth, non-woven fabrics, OHP sheets and so forth. In concrete, the invention is applicable for office equipment, such as a printer, a copying machine, a facsimile machine, mass-production equipment and so forth.
2. Description of Prior Art
Ink-jet printing systems are widely utilized in printers, copy machines and so forth for low noise, low running cost, compact apparatus size, and ease of providing color printing capability.
However, when printing is performed for printing an image on a printing medium, so-called plain paper by the apparatus employing such ink-jet printing system, it is possible to degrade the printed image quality due to lack of water-resistance. Also, upon printing of a color image, in the case that a large amount of ink is ejected for obtaining high density color image, it is possible to cause permeation of the ink into the printing medium to cause feathering. On the other hand, when attempt is made to obtain high density color image with restricting permeation of the ink into the printing medium, bleeding can be caused between adjacent distinct colors. In any of the above-mentioned cases, printing quality in color printing can be significantly degraded.
As a measure for improving water-resistance of the image, it has been practiced in recent years to provide water-resistance for the coloring agent contained in the ink. However, in certain environmental conditions, the water-resistance currently provided for the coloring agent is still insufficient. In addition, in principle, such ink with the water-resistive coloring agent is insoluble to water once it is dried. Therefore, it has high possibility of causing plugging of the printing head. This, in turn, inherently requires complexity of a construction for preventing plugging of the printing head.
As another measure for improving water-resistance, Japanese Laid-Open Patent Application No. 84992/1981 discloses a method to preliminarily coat a material for fixing the coloring agent on the printing paper. That is, it is taught that a large number of specific printing papers each of which is coated with the material for fixing, are previously prepared. However, in this method, it becomes necessary to prepare a specific printing paper. Also, it is unavoidable to cause enlarging in size and cost of an apparatus for preliminarily coating the material for fixing the coloring agent. Furthermore, it is not easy to stably coat the coloring agent fixing material on the printing paper at a predetermined coat layer thickness.
Japanese Laid-Open Patent Application No. 63185/1989 discloses a technology for fixing an achromatic and transparent liquid which makes the coloring agent contained in the ink insoluble, on the printing paper by means of a liquid-jet head. Also, Japanese Laid-Open Patent Application No. 202328/1993 discloses a technology for obtaining a color image without causing color bleeding by employing an ink containing a chemical dye including carboxyl group and polymetal salt solution and by applying the ink after application of the polymetal salt solution to obtain water-resistance.
When the achromatic and transparent liquid for making the dye insoluble is ejected through the liquid-jet head, it is clearly necessary to check whether such achromatic and transparent liquid is normally ejected through all of the ejection openings of the liquid-jet head or not, similarly to that required in normal printing ink. However, a construction to certainly detect ejecting condition of the liquid-jet head for ejecting such liquid has not been available, at the present. Therefore, the only measure currently available is to apply the construction for detecting ejection failure of the printing head for ejecting normal printing ink. Hereinafter, discussion will be given for ejection failure to be caused in the printing head for ejecting ink, a recovery process for the ejection failure-and the conventional construction for detecting the ejection failure.
In the printing operation of an on-demand type ink-jet printing system, all of a plurality of ejection openings provided on one printing head are not always used throughout printing operation. Frequently, non-use ejection openings which are not used for a given period or longer, are present in the ejection head. Also, when a plurality of printing heads are present, such as in a color printing apparatus, it is possible that no printing data is transferred to a certain printing head (ejection is not performed therethrough). In such case, the overall printing head may be placed in non-use condition. In such case, since a cap is held released during printing operation, the ink located in the vicinity of or within the ejection openings which are held in non-use state for a certain period, is inherently dried to cause lowering of ink ejection performance or to cause failure of ejection in the worst case, and thus causes degradation of the printed image quality.
The ejection failure may also be caused by adhesion of ink mist generated in association with ejection of the ink, or paper dust and so forth in the vicinity of the ejection openings.
Furthermore, among ink-jet printing methods, in a system, in which an ejection head is provided in an ink passage portion communicating with the ejection openings of the ink-jet head for generating thermal energy to be utilized for ejection of the ink, the thermal energy is applied to the ink within the ink passage portion to cause film boiling of the ink to perform ejection of ink utilizing growth of a bubble, small bubbles may be accumulated within the ink passage through repeated growth of the bubble. Accumulation of such bubbles in the ink passage may cause interference with supplying of the ink, and possibly cause ejection failure, in which ejection of ink cannot be performed.
As a measure for preventing such ejection failure, it has been proposed, for example, to perform capping for the printing head during non-printing or resting state to prevent the ink from increasing viscosity or solidifying. It is also typical to perform an ejection recovery process for forced discharge of the ink of the increased viscosity or foreign matter around the ejection opening, which cannot be removed by a wiping blade, by means of a suction pump connected to the cap.
Particularly, in case of the ink-jet printing apparatus employing the ink-jet head having a plurality of ejection openings, ejection failure, non-ejection or offset of ejecting direction should result in significant degradation of the printed image quality. Therefore, it becomes necessary to somehow detect ejecting condition of each ejection opening. Such detecting method may be utilized for checking whether a recovery process is necessary or normal ejection is resumed after the recovery process.
Conventionally, as a method for checking the ejecting condition, a method for detecting ejection failure by measuring temperature increase upon ejection of the ink with a temperature sensor provided in the printing head has been known. This method utilizes a fact that heat accumulation in the head is increased when non-ejection failure is caused and whereby temperature increase becomes large. However, in this method, it is possible that ejection failure cannot be detected even when ejection failure is caused at a few number of ejection openings in the head which has relatively large number of ejection openings, e.g. 50 or 100 ejection openings. Therefore, such method cannot provide precision for enabling judgment whether ejection is performed or not with respect to each individual ejection opening.
Also, there has been known a method for detecting whether the ink ejection failure is caused or not by detecting an ink droplet ejected from each ejection opening with an optical sensor. However, such method inherently causes an increase in cost.
As the simplest method for detection of ejection failure, Japanese Laid-Open Patent Application Nos. 261078/1986 and 261079/1986 disclose methods for performing a predetermined pattern which is prepared for checking ejecting condition of each ejection opening, on the printing medium and for visually making judgment. This method is effective for the colored ink since the printed image is visible. The method surely enables the ejection failure of the ink-jet head ejecting a colored ink to be detected because the ink is visually checked. However, in case of the liquid-jet head ejecting a light colored liquid or an achromatic and transparent liquid, it is difficult to visually check the printed image. Therefore, in this method, ejection failure cannot be detected for the ejection openings ejecting the hypochromic or transparent liquid.
Also, when the ejection failure cannot be detected, it is possible to cause not only degradation of the printed image, but also increasing of consumption of the liquid because of unnecessarily performing the suction recovery operation even when ejection failure is not actually caused.